Transporting a liquid past a barrier

Abstract

The invention provides a method of transporting a liquid A past or around a barrier, by adding a solute S to liquid A on one side of the barrier and correspondingly removing solute S from liquid A on the other side of the barrier, the solute S being such as to change the density of the liquid A when dissolving in it, thereby providing a motive force for its motion around the barrier. An example of the application of the invention is in a two-part electrolytic cell (1) comprising electrowinning and electrofining half cells (2 and 3, respectively), wherein the metal, solute S, is electrowon into a liquid (16,16a), liquid A, on one side of the cell's common electrode (4), the barrier, in the electrowinning half cell (2), and electrolytically removed from the liquid (17,17a) on the other side of the common electrode (4), in the electrorefining half cell (3).

I claim: 
     
       1. A method of transporting a liquid A past a barrier, the method comprising: providing liquid A on both a first and a second side of the barrier, the liquid A on the first side being in hydrostatic communication with that on the second side both over and under the barrier, and liquid A on at least the second side of the barrier containing a solute S, solute S being a metal and solute S being such that increasing the concentration of solute S in liquid A either (a) increases or (b) decreases the density of the solution; and introducing solute S into liquid A on the first side of the barrier and removing solute S from liquid A on the second side of the barrier, whereby to cause passage of liquid A around the barrier, with S-rich liquid A from the first side passing under the barrier and S-depleted liquid A from the second side passing over the barrier in case (a), and S-rich liquid A from the first side passing over the barrier and S-depleted liquid A from the second side passing under the barrier in case (b). 
     
     
       2. A method according to claim 1, wherein liquid A is a metal. 
     
     
       3. A method according to claim 1, wherein solute S is introduced into liquid A on the first side of the barrier electrolytically. 
     
     
       4. A method according to claim 1, wherein solute S is removed from liquid A on the second side of the barrier electrolytically. 
     
     
       5. A method according to claim 1, wherein a liquid of relatively low density LD hydrostatically connects the upper surface of a body of liquid A which extends downwardly from the top of the barrier on one side of the barrier with the upper surface of a body of liquid A which extends upwardly from the bottom of the barrier on the other side of the barrier, and a liquid of relatively high density HD hydrostatically connects the respective lower surfaces of those two bodies of liquid A. 
     
     
       6. A method according to claim 1, wherein there is a constriction at the top and/or at the bottom of the barrier, to control the rate of transport of liquid A. 
     
     
       7. A method according to claim 1, when performed in the course of the electrolytic production of a metal M in an electrolytic cell which comprises an electrowinning half cell and an electrorefining half cell, the barrier separating the two half cells, and during operation of the cell the liquid A dissolving metal, acting as solute S, produced in the electrowinning half cell, and being transported past the barrier to the electrorefining half cell, where dissolved metal is removed from the liquid A and electrorefined. 
     
     
       8. A method according to claim 7, wherein the barrier is electronically conductive and acts as a common electrode for the electrowinning and electrorefining half cells. 
     
     
       9. A method according to claim 8, wherein the liquid A is electronically conductive and is electrically in contact with the common electrode barrier. 
     
     
       10. A method according to claim 9, wherein the liquid A wets the common electrode barrier. 
     
     
       11. A method according to claim 9, wherein the common electrode barrier is inclined such that it overhangs liquid A passing under it and projects under liquid A passing over it. 
     
     
       12. A method according to claim 7, wherein the liquid A is electronically conductive and is electrically in contact with the common electrode for the electrowinning and electrorefining half cells. 
     
     
       13. A method according to claim 7, wherein the metal produced in the electrolytic cell is lithium. 
     
     
       14. A method according to claim 13, wherein liquid A comprises aluminium. 
     
     
       15. A method according to claim 14, wherein the barrier comprises a refractory hardmetal, preferably titanium diboride. 
     
     
       16. A method according to claim 13, wherein the electrolyte in the electrowinning half cell comprises lithium carbonate, and the anode reaction in the electrowinning half cell is   2CO.sub.3.sup.= +C=3CO.sub.2 +4e.     
     
     
       17. A method according to claim 7, wherein the metal produced in the electrolytic cell is magnesium. 
     
     
       18. A method according to claim 17, wherein liquid A comprises aluminium. 
     
     
       19. A method of transporting a liquid A past a barrier, the method comprising: providing liquid A on both a first and a second side of the barrier, the liquid A on the first side being in hydrostatic communication with that on the second side both over and under the barrier, and liquid A on at least the second side of the barrier containing a solute S, solute S being such that increasing the concentration of solute S in liquid A either (a) increases or (b) decreases the density of the solution; and introducing solute S into liquid A on the first side of the barrier and removing solute S from liquid A on the second side of the barrier, whereby to cause passage of liquid A around the barrier, with S-rich liquid A from the first side passing under the barrier and S-depleted liquid A from the second side passing over the barrier in case (a), and S-rich liquid A from the first side passing over the barrier and S-depleted liquid A from the second side passing under the barrier in case (b), wherein a liquid of relatively low density LD hydrostatically connects the upper surface of a body of liquid A which extends downwardly from the top of the barrier on one side of the barrier with the upper surface of a body of liquid A which extends upwardly from the bottom of the barrier on the other side of the barrier, and a liquid of relatively high density HD hydrostatically connects the respective lower surfaces of those two bodies of liquid A. 
     
     
       20. A method according to claim 19, wherein the barrier is inclined such that it overhangs liquid A passing under it and projects under liquid A passing over it.